The present invention relates to the field of fabricating retaining walls in the ground, and of retaining works made up of a plurality of retaining walls.
More particularly, the invention relates to a method of fabricating a retaining wall with the help of a technique of digging earth and mixing it up in situ with a binder (known as “soil-mixing”). In known manner, that technique consists in in situ mixing earth with a binder in order to constitute treated soil elements, presenting mechanical and/or geotechnical characteristics that are better than those of the natural non-treated earth. To do this, appropriate tooling is used, such as that described in document WO 2007/116178 or FR 2 879 632.
Such machines serve to make untreated walls in the ground, and more generally continuous structures of treated soil constituted by repeatedly passing the tooling in juxtaposed excavations.
It is also known to excavate a volume of ground adjacent to the untreated wall in order to uncover a surface of the untreated wall, after which said surface is in the open air.
The material that results from mixing the soil in situ with the binder presents the advantage of requiring less natural resources in order to be performed.
Nevertheless, since the resulting material is produced by mixing, it presents characteristics that are very different from those of concrete: the material is much less strong, it is very non-uniform, it presents micro pores, and it provides less protection than concrete for any reinforcement that might be embedded in the untreated wall.
A large difference between concrete and the material that results from the mixing (referred to as soil-mix) is its porosity. Whereas concrete has porosity lying in the range 5% to 15% by volume, a soil-mix material presents porosity lying in the range 30% to 65%. It is known that the greater the porosity of a material, the greater the rate at which said material is degraded.
When the soil-mix material is exposed to air, the above-mentioned micro-porosity, which is four to five times greater than that of concrete, leads to phenomena of drying and of carbonation that degrade the mechanical characteristics of the material.
That phenomenon is extremely troublesome for retaining wall applications, since the material can become degraded very quickly.
In order to solve that problem, it might be envisaged to provide a web of reinforced concrete having a thickness of several tens of centimeters on the exposed surface in order to improve the mechanical characteristics of the wall. Specifically, that way it would make it possible to withstand forces applied against the untreated wall while preventing degradation of the mechanical characteristics of the material constituting the untreated wall.
A drawback of that technique is that it increases the thickness of a retaining work considerably, thereby leading to a loss of available space inside the work. For example, when the retaining work is in an underground car park, it can be understood that the volume available for making the car park would be significantly reduced by the large thickness of the walls, which is undesirable.
Document JP 2001 032235 describes a similar method in which a layer of concrete is applied to the uncovered surface in order to prevent erosion to the banks of a canal.